Electrophotographic imaging members, e.g., photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment move under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible toner image by depositing oppositely charged toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Toner utilized in development in the electrographic process is generally prepared by chemical toner processes, more specifically, mixing nanometer size emulsion polymer and latex with a color pigment and other toner components during an aggregation process, followed by a coalescence process, in which the various components are bonded together. A thermoplastic binder resin may be used in the aggregation process and may be several known polymers, such as polystyrenes, styrene-acrylic resins, styrene-methacrylic resins, styrene-butadiene resins, polyesters, epoxy resins, acrylics, urethanes and copolymers thereof. Carbon black is a common pigment used for toner compositions. Colored pigments such as red, blue, green, cyan, magenta, yellow, brown and mixtures thereof, may also be used. Other toner components my be included, for example, wax and charge enhancing additives.
As known in the art, an “emulsion” generally refers to a dispersion of one liquid in a second immiscible liquid. A “suspension” generally refers to a mixture of two substances, for example a solid and a liquid, one of which is finely divided and dispersed in the other. A “pre-suspension” is the stage of mixing the two substances before they reach a sufficient degree of dispersion in one another to be considered a suspension. “Homogenizing” is used to generally refer to the manner of breaking particles down mechanically until they are consistently dispersed or distributed throughout a liquid
There are known processes and devices for preparing toner components used in toner compositions, especially color pigment dispersion and wax dispersion. For example, there are processes for pigment dispersion for preparation of toner compositions, as generally disclosed in reference U.S. Pat. No. 4,883,736, and U.S. Ser. No. 11/155,452 to Chung et al., filed Jun. 17, 2005, the disclosures of which are totally incorporated herein by reference. Examples of commercially known processes include the melt blending of the toner components in a BANBURY twin screw extruder compounder (available from Farrel Corpoation, Ansonia, Conn.), and in a dispersion of pigment and wax in aqueous phase in a batch stirred tank.
Currently, a batch process is most commonly used for the preparation of toner components such as color pigments and wax. The batch process is used to prepare the color pigment or wax dispersion in an aqueous phase, which involves a high temperature emulsification of molten wax stirred in a vessel followed by homogenization in a homogenizer, such as for example, a Gaulin homogenizer. Multiple passes through the homogenizer is required to obtain the desired level of emulsion to ensure uniformity and size. However, even though the batch process involves long processing time and consumes a great deal of energy to run the process throughout, this process does not ensure the desired level of uniformity and aggregation of the produced toner component. In fact, it is difficult to produce batch-to-batch consistency and scale-up the batches due to different batch reactions. In addition, the batch process requires constant attention as an entire batch may have to be aborted if the batch process is out of control in terms of temperature, impeller speed, and the like.
Therefore, there is a need for processes with improved dispersion of toner components used in preparing toner compositions. In addition, there is a need for processes that provide more control of the particles produced, including maintaining quality, uniformity and size, without the extensive time and energy used in more conventional methods.
The term “electrostatographic” is generally used interchangeably with the term “electrophotographic.”